Patent GB-886664-A (GB)
Title: Improvements relating to railway centralised traffic control systems
IPC: B61L7/08
Filed: 1957-04-18
Abstract: 886,664. Railway centralized traffic control systems. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd., and SHIPP, D. G. April 18, 1958 [April 18, 1957], No. 12657/57. Class 105. In a railway C.T.C. system manually-operated switches are associated with respective selected track circuit indications and on operation effect the transmission of a control code to the appropriate field location for causing the associated track circuit, if the track relay thereof is energized (indicating track section unoccupied), to assume a state such that release of the relay is indicated at the control office upon receipt of the appropriate indication code, whereby the said associated track circuit can be tested as to the correctness of the indication of its state or condition received at the control office. As shown, the invention is embodied in the code communication system described in Specification 886,663 of the continuously-scanning type for controls and indications, as applied to a C.T.C. system. The control office equipment is represented on the left of the broken lines and that of a field station on the right of said lines, the control-indication code transmissions taking place between the office and field station over the transmission wires LC. Carrier frequencies f1, f2 constitute the control codes and f3, f4 the indication codes, all frequencies being different, and f2, f4 being used for cases of more restrictive conditions as regards train movement. The frequency transmitters CTf1, CTf2 at the control office and ITf3, ITf4 at the field station are controlled respectively by code selectors CS, FS which determine which of the transmitters is to transmit during a particular scanning step of a cyclic scanning system. If the selector is energized the less restrictive code f1 or f3 is transmitted and if not energized the more restrictive code f2, or f4, is transmitted. The check feature is installed in the system in respect of the selected indications or scanning steps in the same way as would the equipment necessary for performing a control function. Such step in the scanning system is indicated at the control office as the stage CCx, the stage of the corresponding step at the field station being designated FCx. An output line from the stage CCx extends over the push-button switch IC to the selector CS, the switch being normally open, and on operation allows an output from the stage CCx to energize the selector. A check relay CK is connected to the corresponding stage FCx at the field station through its associated registry " gate " stage RS, when this latter is conditioned in response to the control code f1, so that when the button IC is held depressed relay CK is energized when the step-by-step scanning reaches the stages CCx and FCx, and remains energized in subsequent scanning cycles until the button is released and control code f2 is transmitted. The indication code transmission is allocated a step, e.g. FCx+2 in the scanning cycle different from the control code transmission step, the indication code transmission control circuit including a front contact TR of the track relay of the track circuit under test and a back contact of the check relay CK, so that on operation of the test button IC the relay CK picks up, and the indication code transmission control circuit to the selector FS is interrupted and the indication code f4 is transmitted instead of f3, this change being detected at the control office by the registry stages RS so that relay TK falls away and the red lamp N is illuminated in place of the green. When the button IC is allowed to return to normal position, relay CK falls away and the transmission control circuit is completed at back contact CK, the front contact TR being made (track unoccupied), and code f3 is transmitted in the appropriate scanning step to pick up relay TR at the control office and illuminate the green lamp G. In normal operation, on occupation of the track section, contact TR would open, thus causing code f4 to be transmitted to illuminate the red lamp R at the control office.